Controlling combustion system of gas-turbine engines



Sept. 8, 1953 A. A. GRIFFITH 2,651,175

CONTROLLING COMBUSTION SYSTEM OF GAS TURBINE ENGINES Filed Sept.' 15, 1947 f 3 Sheets-Sheet l p 1953 I A. A. GRIFFITH 2,651,175

CONTROLLING COMBUSTION SYSTEM OF GAS TURBINE ENGINES Filed Sept. 15, 1947 v 3 SheetsSheet 2 v v f/NVE/WOR AMA A. GAFF/ZH Sept. 8, 1953 A. A. GRIFFITH 2,651,175

CONTROLLING COMBUSTION SYSTEM OF GAS TURBINE ENGINES Filed Sept. 15,. 1947 3 Sheets-Sheet I5 Patented Sept. 8, 1953 CONTROLLING GOIWBUSTION- SYSTEM GAS-TURBINE ENGINES Alan Arnold Griffith, Derby, England, assignor to Rolls-Royce Limited, Derby, England, a British company Application September 15, 1947, Serial No.

In Great Britain September 11, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires September 11, 1966 This invention relates to gas-turbines and a particular application is to turbine-engines used in aircraft propulsion.

In present practice, gas-turbines are usually controlled by adjustment of the rate of fuelsupply only; it is necessary to provide a fairly Wide range of mixture-strength to satisfy various operating conditions, and additionally, large variations of mixture-strength occur during rapid acceleration and deceleration giving rise to various disadvantages and increasing the difiiculty in combustion chamber design. For example, in the case of gas-turbine aero-engines, difficulties have been encountered due to extinction of the flame during acceleration and subsequent difiiculty in relighting, particularly in flight.

According to one feature of this invention, means controlling a gas-turbine comprises a bypass to divert air from entering the combustion chamber and to mix it with the efiiuent gases therefrom, manually operated valve means controlling said by-pass, and thermostat means to control the rate of fuel-supply to the combustioncliamber to give a preselected rise of temperature in the combustion-chamber, that is a preselected rise of temperature between the inlet and outlet of the combustion chamber, or a preselected absolute temperature at or near the outlet.

The control means according to this invention is applicable to any type of combustion-chamber, and to any type of engine in which the power increases as a function of the temperature of admission to the turbine. A particular though not exclusive application is to gas-turbine engines used for aircraft propulsion, whereby a relatively wide range of normal operating conditions is called for, whilst in addition the control-system should be able of dealing with rapid accelerations and decelerations. It is particularly well adapted to the annular types of chamber with centrifugal atomisation, for which the attainment of an adequate range of stable burning is one of the principal problems. It is equally applicable however, to engines in which a number of separate combustion-chambers are .used.

In the application of this invention to any type of gas-turbine, there is provided a by-pass passage which extends from the air-supply conduit, at a point before its communication with the combustion-chamber, to the outlet passage from the combustion-chamber through which the eiiluent gases pass to the turbine, and this by-pass is provided with a controlling valve which, in the preferred construction, is controlled by the operator, and this valve may constitute his only direct control of the engine.

6 Claims. (01. -3933) to the mixture-strength, subject to variations arising from the change in the specific heat of air, partial dissociation of the combustion products taking place at very high temperature or incomplete combustion at mixture-strengths differing considerably from that in which the chamber works most satisfactorily, but by controlling the mixture-strength as a function of the combustion-chamber temperature, stable combustion can be ensured.

The following description which has reference to the accompanying drawings, illustrate the application of this invention to two types of gasturbine-engines.

In the drawings, Figure l is a diagrammatic illustration of a gas-turbine-engine of the type having an annular combustion chamber with centrifugal atomisation.

Figure 2 is a diagrammatic sectional illustration of a gas-turbine-engine having a series of separate combustion chambers, and

Figure 3 is a view similar to Figure 2 showing a modification.

Referring to Figure 1, the engine comprises a turbine-compressor system in which the rotor includes a series of separate contra-rotating discs, each carrying both turbine and compressor blades. The compressor blades l9 deliver air through ducts II to an annular combustion chamber 12 in-which fuel is burnt in the air and from which the combustion products admixed with the air are delivered through ducting I3 to the turbine blades I 4 to drive them.

Mounted centrally within the combustion chamber I2, there is a centrifugal fuel atomiser comprising a stationary shaft [6 carrying a rotatable fuel distributor ll. The fuel distributor carries vanes l8 so that air entering the combustion chamber I2 drives it and a portion of the air flows through an annular passage l9 in the fuel distributor I! to an annular outlet 20 of an annular distributor chamber 2i from a reservoir 22 through conduits 23, a feed space 24 between the shaft [6 and fuel distributor I7 and radial conduits 24 in thefuel distributor.

The fuel-flow to the combustion chamber 12 is varied by means of a thermostatically-controlled valve device 25, the thermostat device 26 being located within the combustion chamber l2, so as to be responsive to temperature-changes in the combustion chamber and to maintain a constant temperature within the chamber I2.

An air by-pass duct 2'! connects the air inlet duct 1 I with the outlet duct 13 and flap-valves 28 a preselected rise of temperature between the inlet and the outlet from the combustion chamhere '32, a pair of thermostat devices 40, 44 are are provided to vary the quantity of air flowing through the combustion chamber 52 where, it is heated to the extent determined by the amount of fuel supplied which is in turn determined by the setting of the thermostat device 26. The

effl l ht gases from the combustion chamber IZ are then mixed with airto produce the desired temperature fol driving the turbine at its idling speed. When more power is required the valve 2's is partly closed and the immediate eife'ct is that a larger proportion of air is directed through the combustion chamber '12. A reduction or the temperature therein immediatmy follows which causes the thermostat device 25 to increase the fuel supply to restore the air-fuel balance so that the combustion chamber i2 is working under the same temperature conditions but with more air and more fuel in the same'proportion. The efiiuent gases are mixed with less b'y-passed air so that the temperature of admission to the turbine l 4 is increased and it therefore accelerates.

When the valves 28 are fullyshut'the whole air-supply goes through the combustion chamber 12 and the temperature of admission to the turbine reaches the combustion chamber temperature as determined by the setting of thethermostat device 23. This is the full "power condition of operation of the engine. Thethermostat may be positioned either in the combustion. chamber as described; or at or near the outlet from the combustion where it will be subject. to the infiuence of the temperature of the effluent gases 'justprior to mixing with the by-p'assed air.

In eifect therefore, the control means of this invention functions to give a preselected "absolute temperature or the eflluent gases in the combustion chamber or at or near the outlet from the combustion chamber.

Referring nowto Figure 2', the engine comprises a compressor 30 delivering air into a distribution chamber 31 from which the air flows to a series of combustion chambers 32' in which fuel is burnt in the air. The eiilnent gases from the combustion chamber pass through outlet nozzles 33' and a nozzle-guide vane assembly St to a turbine 35 to drive it; The turbine '35 drives the compressor 30 through a shaft 36. The combustion chamhere aredisposed in a rin around the shaft 36.

Fuel 'issupplied to the combustion chamber burners 2+1 through supply conduits 38 and the rate of flow of fuel to the burners is varied by a valve device ts the operation of which is controlled-by a thermostat device 40. The latter is located near the outlet from the combustion chambers so as; to be affected by the temperature of the-effluent gasesand thereby controls the fuelsupply to maintain the efliuent gases at a substantially constant temperature;

If it desired tocontrol; the fuel flow to give provided, one near the combustion chamber inlet and one near the combustion chamber outlet. These thermostat devices 40, 44 are arranged to control the valve device 39 thereby to control the fuel fiowto maintain a predetermined temperature 'r'i'se between the inlet and outlet of the combustion chambers 32,

An air by-haSs'cOnduit 4| is connected between the inlet to the combustion chamber 32 and the outlet nozzles 33 and a control valve 42 actuated bythe operators control lever E3 is provided to vary the quantity of air flowing through the byass conduit M and thereby varying the quantity of air passing into the combustion chamber.

Theoperation of the engine is similar to that illustrated in Figure l, with the valve 42 fully open, only partof the air flows through the combustion chambers 32 "where'it is 'heated'to a temperaturedetermined "by the setting of the "thermostat device fifl and the remairrderof the air flows through the'by pass conduit cl and is mixed with the efliuent gases to produce the desired temperature torun the turbine at its idling speed.

Asthe 'v'ai'vetz is closed, the proportion of air flowing through combustion chambers increases but the temperature atjth'e'outl et therefrom remains the same 'clue't'o the action of the thermostat device and the proportion of air flowing throu h "the by-p'asseonduitdecreases so that the temperature of'the eases entering the tm'bine increases, giving mOIE' pO WEI.

With the valve 3'2 fully closedthe whole-of'the air passes through the combustion chambers and is heated to the temp-eramredetermmed by the setting of the thermostat. This is the full power condition of'operati'on of the engine.

With the'proposed sy'stein'of control, the ex tr'eme range of transient 'mhc'ture-strength, assuming that the 'op'erators throttle-valve is moved so quicklythat the thermostat has not time to'op'erate', can beaccurate'ly calculated. The response by the thermostat however usuall take ie ce; suiiicieh'tly ra idly that the actual range of mix'ture strengthsis somewhat narrower than the said eirtren're ran e, so that a margin of safety against accidental extinction is ensured. It has been foundfthat theextreme range of mixture strengths under these conditions is somewhat narrower than the range actually needed to cover all "operating conditions and it can be arranged that; under steady runnihgcon ditions, the mixture-strength is at all timeswith in the range of satisfactorily efficien't combustion.

If desired, an "oven-riding. controloperated by a turbine-driven governor can be used to provide against the possibility'offanyuefeot arising-which effects the normalrelationship between the speed and" the combustion-temperature.

In combustion-chambers in. which primary, secondary and may be tertiaryair inlets are provided, the an-co'ntrolinay beus'ed' to "by-pass" air. appropriately from heor more of the inlets to maintain the mixture strength Within c1 3sired limits.

1 Claim;

1. A gas-turbine engine comprising a compressor, a combustion chamber having. an. inlet connected to receive compressed; air frorn'saidlcome pressor and having an o utletthe'refrom, fuelisupply means arrah'gecfto deliver fuel to said. combustion chamber to heat the air flowing. therein and including a fuel su ply control valve, a bypass conduit connected to receive compressed air from said compressor and connected to deliver the by-passed air to mix with heated air leaving said combustion chamber through its outlet, a turbine connected with the outlet from the combustion chamber and with the outlet end of the by-pass conduit to receive the mixture of bypassed air and heated air; valve means arranged for manual adjustment to control the ratioof the quantity of compressed air entering the combustion chamber to that entering the by-passconduit, said valve means constituting the sole power-selecting control of the engine, and-thermostat means arranged within the combustion chamber to respond to a temperature condition in the combustion chamber and arranged to adjust said fuel supply control valve to vary the supply of fuel to the combustion chamber to maintain said temperature condition in said combustion chamber.

2. A gas-turbine engine comprising a compressor, a combustion chamber having an inlet con nected to receive compressed air from said compressor and having an outlet therefrom, fuel su ply means arranged to deliver fuel to said combustion chamber to heat the air flowing therein and including a fuel supply control valve, a bypass conduit connected to receive compressed air from said compressor and connected todeliver the by-passed air to mix with heated air leaving said combustion chamber through its outlet, a turbine connected with the outlet from the combustion chamber and with the outlet end of the by-pass conduit to receive the mixture of bypassed air and heated air; valve means arranged for manual adjustment to control the ratio of the quantity of compressed air entering the combustion chamber to the quantity of compressed air entering the by-pass conduit, said valve means constituting the sole power-selecting control of the engine, and thermostat means arranged within the combustion chamber adjacent the outlet thereof torespond to the temperature of the heated air leaving the combustion chamber and arranged to adjust said fuel supply control valve to maintain the temperature of the heated air leaving the combustion chamber substantially constant.

3. A gas-turbine engine comprising a compressor, a combustion chamber having an inlet connected to receive compressed air from said compressor and having an outlet therefrom, fuel supply means arranged to deliver fuel to said combustion chamber to heat the air flowing therein and includin a fuel supply control valve, a'bypass conduit connected to receive compressed air from said compressor and connected to deliver the by-passed air to mix with heated air leaving said combustion chamber through its outlet, a turbine comiected with the outlet from the combustion chamber and with the outlet end of the by-pass conduit to receive the mixture of bypassed air and heated air, valve means arranged for manual adjustment to control the ratio of the quantity of compressed air entering the combustion chamber to the quantity of compressed air entering the by-pass conduit, said valve means constituting the sole power-selecting control of the engine, and thermostat means comprising a pair of temperature-sensitive devices arranged within the combustion chamber the one adjacent the outlet from the combustion chamber to respond to the temperature of the heated air leaving the combustion chamber and the other adj acent the inlet to the combustion chamber to respond to the temperature ofthe-air entering the sor, a combustion chamber having an inlet connected to receive compressedair from said compressor andhaving an outlet therefrom, fuel supply meansarranged to deliver fuel to said combustion chamber to heat the air flowing; therein and including a fuel supplyconduit, thermostat means adapted to respond to atemperature condition of the air heated in said combustion chamber, means including a valve device in said fuel supply conduit responsive to the temperature sensed by'said thermostat device and operative to vary the fuel supply to maintain substantially constant the temperature condition of the heated air, a by-pass conduit connected to receive compressed air from said compressor and having an outlet therefrom, a turbine connected with the outlet from the combustion chamber and with the outlet of the by-pass conduit to receive a mixture of by-passed air and heated air, and valve means arranged for manual adjustment to control the ratio of the quantity of compressed air entering the combustion chamber to the quantity of compressed air entering the by-pass conduit said valve means constituting the sole powerselecting control of the engine.

5. A gas-turbine engine comprising a compressor, a combustion chamber having an inlet connected to receive compressed air from said compressor and having an outlet therefrom, fuel supply means arranged to deliver fuel to said combustion chamber to heat the air flowing therein and including a fuel supply conduit, thermostat means positioned in said combustion chambers at its outlet to be subjected to the temperature of the heating air leaving the combustion chamber, means including a valve device in said fuel supply conduit responsive to the temperature sensed by said thermostat device and operative to vary the fuel supply to maintain substantially constant the temperature of the heated air leaving the combustion chamber, a by-pass conduit connected to receive compressed :air from said compressor and having an outlet therefrom, a turbine connected with the outlet from the combustion chamber and with the outlet of the by-pass conduit to receive a mixture of by-passed air and heated air, and valve means arranged for manual adjustment to control the ratio of the quantity of compressed air entering the combustion chamber to the quantity of compressed air entering the by-pass conduit, said valve means constituting the sole power-selecting control of the engine.

6. A gas-turbine engine comprising a compressor, a combustion chamber having an inlet connected to receive compressed air from said compressor and having an outlet therefrom, fuel supply means arranged to deliver fuel to said combustion chamber to heat the air flowing therein and including a fuel supply conduit, a pair of thermostat devices positioned in said combustion chamber, one of said thermostat devices being arranged adjacent the inlet thereof to respond to the temperature of the air entering the combustion chamber and the other being arranged adjacent the outlet to respond to the temperature of the heated air leaving the combustion 

